Not necessarily. Jumping around is fairly common practice for those who seek fast promos in large tech companies, because it's usually a faster track to get up to the higher levels than just grinding in place. It's not all that uncommon to find people who went Microsoft/Amazon/Google/Facebook full circle, for example. And they aren't necessarily unhappy about their past stints. But, again, the recurring theme seems to be that Amazon is the worst of the bunch in terms of hours worked (and work/life balance in general) and career opportunities.